This invention relates to a data randomization equipment for randomizing digital data and to be used for random number generators for generating random numbers of digital data and for encrypting and decrypting processes of cryptographic equipment.
The data randomization equipment will first be briefly described. As shown in FIG. 1, data randomization equipment receives digital input data and digital parameter data and provides randomized data as output data.
High class data randomization equipment requires that nearly one half of the output data bits be changed with a slight change in the input data or parameter data.
The prior art will be described as an example of data randomization equipment which is employed in the DES encrypter as a typical cryptographic equipment. FIG. 2 shows this data randomization equipment. The size of 32-bit input data is expanded by data expanding means 12 into 48-bit data. In this data expansion, the 32-bit input data is split into eight blocks each of 4 bits, and the bits on both sides of each 4-bit block are each branched into two bits.
Exclusive OR part 13 takes exclusive OR between each bit of the expanded 48-bit data and a corresponding bit of 48-bit parameter data. The resultant 48-bit data is split into 8 blocks each of 6 bits, and these data blocks are fed to respective ROMs 14.sub.1 to 14.sub.8 which are commonly termed S boxes. The S boxes 14.sub.1 to 14.sub.8 each provide 4-bit data using the 6-bit input data as an address. The 32-bit data constituting the outputs of all the S boxes 14.sub.1 to 14.sub.8 is fed to a permutation part 15 constituted by a wired circuit. The permutation part 15 effects bit position re-arrangement of the 32-bit input data and yields the resultant output as a randomized output.
In this prior art equipment, with a change in the input to each of the S boxes 14.sub.1 to 14.sub.8, only one bit at the least to 4 bits at the most of the output undergo a change from "0" to "1" or from "1" to "0", that is, 2.5 bits, in average, of the output are changed. This means that with the occurrence of the change of one bit in the input data to the prior art data randomization equipment, only one bit in the least to 8 bits at the most, i.e., only 4 bits in average, of the 32-bit output data are changed. Further, with a change of one bit of the parameter data to this equipment only 2.5 bits of the output data are changed.